Polyisocyanate treatment of polyurethane fibers

ABSTRACT

Elongation is reduced and the tensile strength and elastic properties of preformed elastomeric, polyurethane fibers are improved by subjecting the fibers to a stretching operation which includes treatment in an organic diisocyanate containing solution to effect a chemical cross-linking modification during stretching.

United States Patent [72] inventor Carl John Setzer [50] Field oi Search 8/ i 15.5; Durham, N.C. 260/775 SP; 264/210, 236, 347, 290, 184 [21] Appl. No. 812,412 221 Filed Apr. 1, 1969 1 References Cited [45] Patented Dec. 28, 1071 UNITED STATES PATENTS 1 Assign WWII") P' Y 3,164,439 1/1965 Muhlhausen 8/1 15.5

St. Louis, Mo.

Primary Examiner-George F. Lesmes Assistant Examiner-B. Bettis 54] POLYISOCYANATE TREATMENT OF Attorneys-A. Milton Cornwell, Jr. and Russell E. Weinkauf POLYURETHANE FIBERS 6 Claims, No Drawings ABSTRACT: Elongation is reduced and the tensile strength [52] m 8/1155, and elastic properties of preformed elastorneric, polyurethane 264/2101 264/2361 264/347 264/290 264/184 fibers are improved by subjecting the fibers to a stretching [51 Int. D06"! p rati n i ludes treatment in an organic diisocyanate Dold 5/12 containing solution to efiect a chemical cross-linking modification during stretching.

POLYISOCYANATE TREATMENT OF POLYURETHANE FIBERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a practical process for treating previously formed and dried elastic polyurethane fibers and in particular to a process whereby fibers of the spandex type are treated while in the stretched state with an organic diisocyanate, in solution. This invention further relates to a treating process that yields a spandex fiber with lower elongation at break and improved tensile strength and elastic moduli.

2. Description of the Prior Art SYnthetic elastic fibers have become well known to the consumer and widely employed in the textile industry where they are generally referred to as spandex yarns. Because these fibers have a balance of properties similar to natural rubber, i.e., low extension and recovery moduli, low tenacity and high elongation, they have found end use applications in garments where rubber had formerly been used. Elastic fibers of the spandex type are commonly made by extruding polyurethane polymers in fluid form through a spinning head under such conditions that the resulting fibrous material is converted to an elastic form. The properties of these elastic fibers are determined by the materials that make up the polymer and the spinning process used in forming the fibers. It is well known that elastic fibers maybe formed by dry or wet spinning solutions of polyurethane polymers prepared by reacting diisocyanates such as 4,4-diphenylmethane diisocyanate with lowmolecular weight diols such as polyesters or polyethers and chain extending the isocyanate terminated intermediate with diamines, diols, etc. Although the properties of these spandex fibers are adequate for most commercial applications, as a replacement for rubber, higher tensile and elastic properties would be desirable in order to improve, for example, the holding power of the yarn in garments such as girdles, brassieres, swim suits, and hose tops. Further, commercial spandex fibers have an elongation property of about 500 percent. In most end use applications the high elongation is unnecessary because the covered elastic yarn in the fabrics is flexed over an extension range of only about 200 percent and in many uses, the elastic yarns are covered to hold at a base elongation of about 100 percent by the covering yarns. By holding the yarn to this base elongation, the actual flexing of the elastic core is in an elongation range where the elastic recovery property is highest for a given spandex fiber. It is therefore desirable to have an elastic fiber with improved elastic properties as measured by stretching and recovery modulus in the 200300 percent elongation range. These fibers would then be useful in both covered and uncovered commercial applications.

It has been proposed by Muhlhausen in U.S. Pat. No. 3,l 64,439 to provide a method for improving the physical pro perties by treating finished spandex filaments with a solution of a polyisocyanate. The filaments treated by the method of this invention have an improved tensile strength and the elongation characteristic is improved, i.e., increased to a higher level. It has also been proposed to improve the properties of threads and foils made from polyamides by treating them with polyisocyanates. This treatment results in a diminished water adsorption and increased stiffness of the treated polyamide. The reason for the improvement of polyamides may be due to the action of the NCO groups with the amide groups of the polyamide.

In the above-described process of Muhlhausen it is necessary to lag the unstretched yarn for prolonged periods in order to effect adequate treatment to give the desired properties which is, of course, impractical from a commercial production standpoint. Further, this treatment of the polyurethane yarn gives improvements in both tensile strength and elongation. The improvement in elongation consists of an increase in the level or percent of elongation to about 400 percent or higher.

Thus, while treatment of fibers with polyisocyanate solutions is not new and while attempts have been made to produce spandex yarns with higher moduli having lower elongation by stretching, and/or stretching and heat setting, the stretched yarns return to their undrawn lengths when allowed to relax, no treatment that is practical and economical has been found to yield a spandex fiber with improved tensile strength, improved elastic properties and an elongation of about 200-300 percent.

SUMMARY OF THE INVENTION This invention providesa method for improving the tensile strength and elastic modulus of a previously formed and dried elastic fiber of the spandex type having an elongation at break of about l00-300 percent and preferably 200-300 percent. The process of this invention is accomplished. during the spinning of the fiber in the following steps, in sequence: (1) stretching the spandex fibers at a temperature of 2040 C. and simultaneously treating said filaments with a solution containing an organic diisocyanate, and (2) drying said treated filaments. The process of this invention is both practical and economical since the postfiber-forming treatment is performed under actual spinning conditions of temperature and spinning speeds and while the fiber is in the stretched state. Further, the diisocyanate treatment does not degrade the fiber and imparts permanent changes in elastic properties even after relaxation.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS TI-Ie present invention provides a method for improving the tensile strength and elastic modulus of a previously formed and dried elastomeric fiber having an elongation at break preferably in the range of about 200300 percent and an initial modulus of about 0.04 g./denier by stretching said fibers about 1.0 to 5.0 X, treating said fibers during stretching with a solution containing about 1 to 10 percent by weight of an organic diisocyanate at room temperature for a residence or reaction time of 0.1 to 10 seconds, and drying said treated fibers. The improvement in the fiber is shown by a permanent reduction in denier, lower elongation at break and higher initial and recovery modulus.

The segmented copolymer which makes up the spandex fiber of this invention consists of a high-melting, crystalline segment alternating with a low-melting, amorphous segment. The crystalline high-melting segment may be derived from, for example, a polyurea or polyurethane. The low-melting amorphous segment may be derived from, for example, a polyester or a polyether diol. Although the chemical reaction of treating the spandex fiber with a diisocyanate is not completely identified it is probably a cross-linking reaction with the active hydrogen in the amino, urethane and/or urea portions of the polyurethane molecule.

Any of a wide variety of organic diisocyanates may be employed in the fiber treating reaction including aromatic, aliphatic and cycloaliphatic diisocyanates and combinations of these types. Representative compounds include, for example, hexamethylene diisocyanate, tolylene diisocyanate, mphenylene diisocyanate, l,4-cyclohexylene diisocyanate, and 4,4'-diphenylmethane diisocyanate. Arylene diisocyanates, i.e. those in which each of the two isocyanate groups is attached directly to an aromatic ring are preferred. In solution the diisocyanate concentration may vary in an amount from 2.0 to 10.0 percent and preferably at about 5 percent.

This invention contemplates using diisocyanate solvents which will swell the fiber but will not react with the isocyanate such as, for example, acetone, methylene chloride, carbon tetrachloride, petroleum ether, benzene, toluene, xylene, monomethyl glycol, ether acetate and the like. Benzene was found to be particularly advantageous since it readily dissolves the required quantity of diisocyanate and will not dissolve the fiber. Further, benzene will cause sufficient fiber swelling to aid in the diisocyanate reaction.

It is preferred to treat the fiber with a solution of the diisocyanate while the temperature of the solution is at about the prevailing room temperature. Temperatures in the neighborhood of 20-30 C. have been found to be particularly useful.

Treatment of the spandex fiber with the diisocyanate solution must be done after the fiber is spun, coagulated and dried and while it is in the stretched state in order to have a fiber with permanent properties of improved tensile strength and elastic modulus and an elongation at break of 200-300 percent. The stretched state" means that the filament is under tension or actually stretched in the spinning line 2 to times. Treatment of the fiber while in the stretched state is a critical feature of this invention. In carrying out the reaction between the spandex fiber and the diisocyanate, the stretched filament is guided into and through the diisocyanate solution at such a rate that the residence time is from 0.1 to 10.0 seconds and preferably about 0.2 to 0.5 seconds.

In order to better describe and further clarify the invention the following illustrative examples are given.

EXAMPLEl This example is the control example to illustrate the preparation of a typical polyurethane, wet spinning the polymer, and the fiber properties obtained.

An elastomeric polymer was prepared by reacting 230 grams of polytetramethylene glycol of 1,800 molecular weight with 65.6 grams of 4,4'-diphenylmethane diisocyanate in 154.6 grams of dimethylformamide solvent at about 30 C. for 1 hour to form a prepolymer. The prepolymer was then slowly added to a solution of 7.2 grams of carbodihydrazide dissolved in 660 grams of dimethylformamide at 20 C. until 308.5 grams of prepolymer was added. This solution or spinning dope was then wet spun into fibers by extrusion through a hole spinneret into a 50 percent water-50 percent dimethylformamide coagulation bath. The elastic filament under minimum tension was passed through a hot (90 C.) water wash zone and then over drying rolls at 135 C. The dried fiber was taken up and fiber properties determined. The properties are given as the control in table 1.

EXAMPLE ll This example illustrates the effect on fiber and fiber properties when the elastic filament from example I is passed through a benzene bath with no diisocyanate present while in the stretched state.

The spinning dope from example I was extruded through a 15 hole spinneret into a 50 percent water-50 percent dimethylformamide coagulation bath, washed and dried by passing the filament continuously through a hot water bath and around a drying godet. The dried fiber was then passed through a benzene bath at about 25 C. and a residence ime of 0.2 seconds while stretching the elastic filament 2.14 times. The fiber was dried and recovered on a takeup roll. The fiber properties are given as the stretched fiber control.

EXAMPLE 111 This example illustrates the invention by treating the elastic fiber from example 1 in a benzene solution as described in ex- TABLE 1 Stretched liber Stretched treated liher with (ontrul with Ml)l (5%) Samples liher benzene in benzene Stretch v None 2.14)( 114x Tenacity g./d O. 70 11,76 1. 30 Elongation. perconL. 465 435 J65 Extension modnlns, g.

50% 2nd eyele 0. 025 ll. 0'20 0. 04; 150% 2nd eyele (I. 00'. 0. 073 0. 134 lteenvery nnnllllus g., rl., 50% 12nd eyele 0. 017 0. (H7 0.021 Stress r1 lenlinn' 50% extension 1 4 eyeles 77 74 74 15H";v extension '24 t les .15 .14 1 4 511"}, reenvery 3'4 eyeles. J4 .14 111i ample 11 except the benzene contained 5 percent 4,4'-diphenylmethane diisocyanate. The fiber properties are given in table 1 as the treated fiber.

The 50 percent extension modulus, 2nd cycle, is the modulus of the fiber in grams per denier at 50 percent elongation with an extension rate of percent per minute and the reading taken after completion of the 2nd 50 percent extension.

From the above data it is readily apparent that diisocyanate treatment of dried elastic fiber in the stretched state yields an elastomeric fiber with higher tensile strength, elongation in the 200-300 percent range, improved elastic properties (extension and recovery moduli) without any impairment of the elastic recovery as shown by the stress retention values.

EXAMPLE IV This example illustrates the invention with a fiber from a polyester derived polyurethane treated with tolylene diisocyanate in methylene chloride.

A prepolymer was prepared by reacting 400 grams of polycaprolactone molecular weight of 2,300 with 87 grams of 4,4-diphenylmethane diisocyanate in 163 grams of dimethylformamide at 2530 C. for 1.5 hours. Prepolymer solution (503 grams) was diluted with 440 grams of dimethylformamide and 848.4 grams of the diluted prepolymer was added to a solution of 7.2 grams of ethylene diamine in 1,330 grams of dimethylformamide to yield a spinning dope having a solution viscosity of 8,000 centipoise.

The spinning dope was extruded into fiber, washed and dried prior to passing the filament into a treating bath consisting of 3 percent tolylene diisocyanate in methylene chloride solvent. The residence time in the treating bath was about 1.0 second and the fiber was stretched 3.5 X during treatment. The treated fiber was then dried, taken-up and the physical properties evaluated. The fiber has the properties of high tensile strength, elongation in the 200-300 percent range and improved elastic properties.

Although the invention has been described in considerable detail for the purpose of clarification, it is to be understood that such detail is solely for this purpose and that variations can be made by those skilled in the art without departing from the spirit or scope of the invention except as set forth in the claims. The invention has been described with respect to a fiber, but it is understood that the invention contemplates various types of films and threadlike structures including filaments, threads, films, coatings, impregnations, and the like.

What is claimed is:

l. A process of treating elastomeric polyurethane filaments to reduce substantially the break elongation thereof comprising the steps of:

a. stretching the said polyurethane filaments about 1.0 to

b. while stretched, treating the filaments for about 0.1 to 10 seconds with a diisocyanate solvent solution containing from 1 to 10 percent by weight of an organic diisocyanate; and

c. drying the thus treated filaments while in the stretched state;

whereby the break elongation of said filaments is substantially reduced to 200-300 percent.

2. The process of claim 1 wherein the organic diisocyanate is 4,4'-diphenylmethane diisocyanate.

3. The process of claim 1 wherein the organic diisocyanate is tolylene diisocyanate.

4. The process of claim I wherein the diisocyanate solvent is benzene.

5. The process of claim 1 wherein the diisocyanate solvent is methylene chloride.

6. A process of treating wet spun elastomeric filaments of a segmented polyurethane copolymer consisting of a high-melting, crystalline segment alternating with a low-melting amorphous segment to reduce substantially the break elongation thereof comprising the steps of:

a. stretching the said polyurethane filaments about 1.0 to c. drying the thus treated filaments while in the stretched 5.0 X; state;

ZS FSf 'x g gigf fzgfggf jlf igi 3 whereby the break elongation of said filaments if substanseco s m a c sov 10 a1 from 1 to 10 percent by weight of an organic diiso- 5 reduced to 200400 Percen" cyanate', and r 

2. The process of claim 1 wherein the organic diisocyanate is 4, 4''-diphenylmethane diisocyanate.
 3. The process of claim 1 wherein the organic diisocyanate is tolylene diisocyanate.
 4. The process of claim 1 wherein the diisocyanate solvent is benzene.
 5. The process of claiM 1 wherein the diisocyanate solvent is methylene chloride.
 6. A process of treating wet spun elastomeric filaments of a segmented polyurethane copolymer consisting of a high melting, crystalline segment alternating with a low-melting amorphous segment to reduce substantially the break elongation thereof comprising the steps of: a. stretching the said polyurethane filaments about 1.0 to 5.0 X; b. while stretched, treating the filaments for about 0.2 to 0.5 seconds with a diisocyanate solvent solution containing from 1 to 10 percent by weight of an organic diisocyanate; and c. drying the thus treated filaments while in the stretched state; whereby the break elongation of said filaments is substantially reduced to 200-300 percent. 